Pearl protein (nacrein) and process for producing the same

ABSTRACT

A nacrein protein is expressed by separating a protein fraction having a molecular weight of sixty thousand, as determined by SDS-PAGE, from pearl proteins extracted from the nacreous layers of pearl oysters, synthesizing a probe coding for the N-terminal amino acid sequence of the protein in this fraction, cloning the cDNA derived from the mRNA of the mantle of the pearl oyster and hybridizable with the synthesized probe, and introducing the cloned cDNA into the host cells of Escherichia coli.

This application has been filed under 35 U.S.C. 371 from PCT/JP96/01236, filed May 9, 1996, which claims priority to Japanese Patent Application 7-110877, filed May 9, 1995.

TECHNICAL FIELD

The present invention relates to proteins of constituting the pearl (pearl proteins), especially, to nacrein proteins produced through the genetic engineering techniques, and to a process for producing and expressing the proteins.

BACKGROUND ART

Shell of the pearl layer in the pearl oyster is consisting of minor proteinic organic matrix and crystal of aragonite. This organic matrix had been designated as "Conchiolin" (Fremy, M. E., Recherches chimiques sur les os. Ann. Chem. Phys, 43, 96 (1855)) and have been studied by many persons since then in all its aspects.

See, for example, the publications of:

(1) Cariolou, M. A. & Morse, D. E., "Purification and Characterization of calcium-binding conchiolin shell peptides from the mollusc, Haliotis rufescens, as a function of development", J. Comp. Physiol. B, 157, pp. 717-729 (1988);

(2) Samata, T. & Krampitz G, "Ca-binding polypeptides in oyster shells", Malacologia 22, pp. 225-233 (1981);

(3) Samata, T., "Ca-binding glycoproteins in molluscan shells with different types of ultrastructure", The Veliger 33, pp. 190-201 (1990);

(4) Koji WADA, "Pearl", Association of Jewelogy of Japan (1982);

(5) Weiner, S. & Hood, L., "Soluble protein of the organic matrix of mollusk shells: a potential template for shell formation", Science, 190, pp. 987-989 (1975);

(6) Weiner, S. & Lowenstam, H. A., "Discrete molecular weight components of the organic matrices of mollusc shells", J. exp. mar. Biol. Ecol., 30, pp. 45-51 (1977);

(7) Weiner, S., "Aspartic acid rich proteins: major component of the soluble organic matrix of mollusc shells", Calicif. Tissue Int., 29, pp. 163-167 (1979); and

(8) Weiner, S., "Mollusk shell formation: isolation of two organic matrix proteins associated with calcite deposition in the bivalve, Mytilus calfornianus", Biochemistry, 22, pp. 4139-4145 (1983).

Up to date, although it was reported that one of the main components in the organic matrix of the pearl layer is asparatic acid rich acidic protein in the molecular weight of 50˜70 kD [See, publications (3) and (7) listed above], its accurate molecular weight and the amino acid sequence thereof have not been reported at all.

Accordingly, as a popular technology for forming pearl wherein a part of shell of Pinctada fucata is coaggulated, cultivation methods depending on environmental (cultural) conditions have been employed over one century or more to cultivate Pinctada fucata for one to two year(s) in a hanging sack in the sea.

DISCLOSURE OF INVENTION

The present invention is established to solve the problems noted above. That is to say, in addition to the genetical study/analysis of the pearl proteins, it is aimed to artificially produce the pearl proteins based on the unique genetic information of such proteins.

At the first step, the inventor extracted the substantial proteins from the natural pearl, purified them and isolated an acidic protein (nacrein) in the molecular weight of approximately 60,000 which is one of the major elements of the proteins and have Ca²⁺ (calcium ion) binding activity. Then, the N-terminal amino acids sequence of this protein was determined, then DNA probes corresponding to the sequence was synthesized.

On the other hand, cDNA library was constructed by extracting mRNA from mantle tissues of Pinctada fucata involved with production of the natural pearl layer. cDNA of nacrein was cloned from this library by a hybridization technique utilizing the synthesized DNA probes noted above.

Then, the nacrein was produced according to the known technique by linking cDNA so obtained to a gene expression vector and introducing the vector into host cell like E. coli. Watabe and Wilbur had already reported that the crystal of aragonite would be specifically produced on the organic matrix of the pearl layer (Watabe N. and Wilbur K. N., "Influence of the organic matrix on crystal type in Molluscs", Nature 188, 334 (1960)). Further, in view of the facts that the nacrein is one of the essential elements of the organic matrix and is the protein having Ca²⁺ -binding activity, in vitro production of the pearl layer will be realized by crystallizing the calcium carbonite to aragonite on the protein.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a scheme showing an outline for extraction, concentration and purification of the nacrein proteins.

FIG. 2 is a graph showing an elution curve of the nacrein proteins obtained by DEAE-Sephacel Column Chromatography.

FIG. 3 is a graph showing an elution curve of the nacrein proteins in the sample to be ion-exchanged obtained by DEAE-Sephacel Column Chromatography.

FIG. 4 is a graph showing an absorbance utilizing Stains-all on the eluted fractions referred to in FIG. 3.

FIG. 5 shows a result obtained by performing SDS-PAGE on the fractions 31 and 40 and staining them with Coomassie Brilliant Blue G-250.

FIG. 6 shows a result obtained by performing SDS-PAGE on the fractions 31 and 40 and staining them with Stains-all.

FIG. 7 is a graph showing an elution pattern obtained at G75 gel filtration of the nacrein proteins.

FIG. 8 shows a result of SDS-PAGE on the samples purified by G75 gel filtration.

FIG. 9 is a detail of CλN6.

FIG. 10 reveals homology between the amino acids of the nacrein and that of the carbonic anhydrase.

FIG. 11 illustrates an insertion of an open reading frame of the nacrein cDNA into NdeI-EcoRI site of the plasmid pT7-7.

FIG. 12 shows a result of SDS-electrophoresis conducted on the nacrein proteins expressed in E. coli with a genetic engineering technique.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail along with the Examples, but the inventions should not be limited based on the disclosure of such Examples.

EXAMPLE 1 Extraction and Purification of Nacrein Protein

Extraction, concentration and purification of the nacrein protein was performed along with the procedures schematically shown in the FIG. 1.

1 Extraction and Concentration of Protein Sample

Clean pearls were selected from crude pearls and nucleus of the pearls were removed. Then, approximately 50 g of powdered strating materials were prepared by isolating pearl layers and crushing them with a pestle. 250 ml of 0.3M ethylenediaminetetraacetic acid (EDTA, pH 8.0) containing 0.01% sodium azide was added to the starting materials, then a mixture was shaked for about three days at room temperature, and soluble organic matrix was extracted therefrom.

This extracted solution was centrifuged at 30,000 g for 20 minutes. Supernatant thereof was poured into a dialysis tube (Spectropore 6, Separation Molecular Weight=2,000) and was dialyzed with H₂ O at 4° C. for 24 hours (H₂ O of outer dialysis solution was changed twice). Then, each of approximately 50 ml of inner dialysis solution was poured into an egg-plant type flask and was lyophilized. Lyophilized samples were dissolved in approximately 8 ml of 10 mM Tris Buffer (pH 8.0) and the products so obtained were used as samples for an ion-exchange chromatography.

2 Purification of Nacrein Protein

4 ml of aforementioned sample was poured into DEAE-Sephacel Column (.O slashed.15 mm×120 mm) equilibrated with 10 mM EDTA solution (pH 7.0) and the proteins in the sample was adsorbed thereby. After washing the column with EDTA solution, extraction was performed with a linear gradient (400 ml) of 0˜0.8M sodium chloride (10 mM EDTA, pH 7.0) and extracts were collected as 8 ml fractions. FIG. 2 shows an extraction pattern obtained by the chromatography of these fractions. In FIG. 2, the solid line is directed to an absorbance at 280 nm wavelength, while the dot line is directed to a quantitative curve on proteins by TCA method (μ=340 nm).

On the other hand, similar chromatography was also performed on 4.5 ml of the remaining sample. In the chromatography, similar extraction curve (FIG. 3) like that referred to in FIG. 2 was observed, and an adsorbence pattern (μ=570 nm) with Stains-all on each extacted fraction is shown in FIG. 4 as the dot line.

Further, SDS-PAGE (8˜16% gradient) on the fractions 31 and 40 were performed. These fractions are corresponding to an absorbence peak by TCA method on the extracts fractions. Samples were then stained with Coomassie Brilliant Blue G-250 (FIG. 5) and Stains-all (FIG. 6).

With reference to FIGS. 5 and 6;

Lane 1 is directed to samples isolated by Drs. Miyashita and Matsushiro (10 μl)

Lane 2 is directed to samples for the ion-exchange noted above (25 μl);

Lanes 3 and 6 are directed to the proteins for molecular weight marker [Myosin (Molecular Weight: 200,000), β-galactosidase (Molecular Weight: 116,300), Phosphorylase (Molecular Weight: 97,400), Bovine Serum Albumin (BSA, Molecular Weight: 66,300), Glutamate Dehydrogenase (Molecular Weight: 55,400), Lactate Dehydrogenase (Molecular Weight: 36,500), Carbonic Anhydrase (Molecular Weight: 31,000), Soybean Trypsin Inhibitor (Molecular Weight: 21,500), Lysozyme (Molecular Weight: 14,400), Aprotinin (Molecular Weight: 6,000)];

Lane 4 is the fraction 31 (25 μl);

Lane 5 is the fraction 40 (25 μl);

Lane 7 is the ten-times concentrated fraction 31 (25 μl); and

Lane 8 is the ten-times concentrated fraction 40 (25 μl).

Based on the results above, the peak fractions 29˜33 obtained at the first ion-exchange chromatography and the peak fractions 21˜25 obtained at the second ion-exchange chromatography were mixed, and poured the mixture into one dialysis tube (Separation Molecular Weight: 2,000). The mixture was dialyzed overnight at 4° C. together with 10 mM EDTA solution (pH 7.0) as on outer solution. After the dialysis, the samples were adsorbed by DEAE-Sephacel Column in which the inner solution (approximately 100 ml) is equilbrated with 10 mM EDTA. Then, the nacrein protein was directly eluted with 0.8M sodiumchloride (10 mM EDTA) solution. Eluted solution (approximately 10 ml) was concentrated to 2 ml of volume with Ultra Free C-20 (Milipore, Separation Molecular Weight: 10,000) and the concentrated solution was employed as a sample for a gel filtration.

Sephadex G75 was employed for the gel filtration. The sample was added to the G75 Column (.O slashed.20 mm×950 mm) equilibrated with 10 mM EDTA and 0.2M sodium chloride solution (pH 7.0), and was eluted with the same buffer at a flow rate of 12.5 ml/hr. Eluted solution was collected as fractions of 3.5 ml. FIG. 7 is an extraction pattern by G75 gel filtration. In the figure, the solid line is directed to an absorbance at 280 nm wavelength, while the dot line is directed to an absorbance by TCA method at 340 nm wavelength.

26 ml of a mixture consisting of peak fractions 37˜43 at TCA method fractioned by G75 gel filtration was employed as final purified products. These products form a single band on SDS-PAGE (See, FIG. 8). Then, when the products were quantitated according to TCA method together with BSA as a standard protein, concentration of approximately 20 μg/ml was confirmed. Accordingly, total purified proteins were calculated at 26×20≈500 μg. 5 ml of the purified products were concentrated to 0.45 ml with Centricon 10 (Amicon; Separation Molecular Weight=10,000) and the concentrated products were employed as a sample for a N-terminal amino acids sequencing.

3 Discussion

In this purification step, besides minor band like a 37 kD protein, major two protein bands at the molecular weight of approximately 60 kD and 15 kD had been detected in the solution of crude extructs from pearl (See, FIG. 5).

Then, when the crude solution is concentrated and the concentrated solution is applied to a chromatography equipped with an anion-exchange resin DEAE-Sephacel, most of the proteins were gotten in one particular peak. Results of SDS-PAGE on this fraction indicate that this fraction is corresponding to proteins in the molecular weight of approximately 60 kD (See, FIG. 5). Further, because of high stainability with Stains-all thereof, the proteins seems to be Ca²⁺ -binding proteins (See, FIG. 6). [K. P. Campbell, D. H. MacLennan & A. O. Jorgensen, "Staining of the Ca²⁺ -Binding Proteins, Calsequestrin, Calmodulin, Troponin C, and S-100, with the Cationic Carbocyanin Dye "Stains-all", J. Biol. Chem., 258 (18), pp. 11267-11273 (1983)]. The protein of 60 kD molecular weight also formed a single peak on the gel filtration utilizing Sephadex G75 as a carrier (FIG. 7).

Accordingly, the protein designated as "nacrein" of 60 kD molecular weight is one of the major proteins of the pearl layer and is acid protein (of binding to the anion-exchange resin DEAE Sephacel) with Ca²⁺ -binding activity.

On the other hand, although the proteins in the molecular weight of 15 kD is also one of the major protein of the pearl layer, it is basic protein (of not binding to the DEAE Sephacel but passing therethrough) without Ca²⁺ -binding activity.

EXAMPLE 2 N-Terminal Amino Acids Sequencing of Nacrein Protein

Foregoing concentrated samples (0.45 ml) were divided into seven lanes to be 25 μl/lane and were applied to SDS-PAGE and an electrophoresis. Then, membrane film containing 60 kD band was excised and was electrically transferred as blotting samples to PVDF membrane filter (Immobilon P).

Then, the transferred membrane was stained with 0.03% Coomassie Brilliant Blue R-250 and the membrane films containing a target band were excised. The films were then set on the blotting sequencer (Type 477A: Applied Biosystems). N-terminal amino acids of the nacrein protein adhered to the films were analyzed twice, and the amino acids sequence was deduced as follows (SEQ ID Nos.:1 and 2).

    Ala Ser Met Phe Lys Met Asp Xaa Tyr Met Asp Xaa Gly Xaa Arg(SEQ ID NO:1)

    Xaa His Met Phe Lys His Asp His Tyr Met Asp Asp Gly Val Arg(SEQ ID NO:2)

At the early stage, to deduce the amino acids sequence was difficult, because the final product have not been purified completely and there were differences in the analysis of first and second amino acids in the N-terminal sequence between first and second determination results thereon. But, in view of the other analysis data and facts that nearly all of third through fifteenth amino acids of the N-terminal sequence were coincided between the first and the second determination results, the N-terminal sequence was determined as the following sequence (SEQ ID No.:3).

    Ala Ser Met Phe Lys His Asp His Tyr Met Asp Asn Gly Val Arg(SEQ ID NO:3)

EXAMPLE 3 Cloning of Nacrein cDNA

(1) Synthesis of DNA probes corresponding to N-terminal amino acids

Base sequence (SEQ ID No.:4) of sense DNA strands was designed with a code table based on amino acids sequence noted above.

44 mer of the following anti-sense DNA strands corresponding to the base sequence is synthesized with DNA synthesizer (No. 392; Applied Biosystems). Alkaline phosphatase is labelled to this probe DNA with DIG oligonucleotide 3'-end labeling kit (Boehringer).

(2) Extraction of mRNA from Mantle Pallial of Pinctada fucata

About one hundred Pinctada fucata of being cultured were got in Uwazima, Ehime Prefecture, Japan, and several experts excised therefrom the mantle pallial which are just forming the pearl layer. Strips of the excised pallials were then immediately sunk in the phosphorus buffer and were lyophilized instantly with liquid nitrogen. Strips from twenty Pinctada fucata were combined and were poured into one polyethylene tube for a centrifugation. After that, the tubes were transported with frozing them by dry ice and have been stored in the deep freezer under the temperature of -80° C.

6M guanidine thiocyanate solution was added (in the proportion of 1:10) to these freezed strips and were crushed with a homogenizer (Polytoron). Whole RNA was extracted from these crushed samples by guanidine-phenol-chloroform method (AGPC method). Approximately 3 mg of RNA was gotten from a single centrifugation tube (including mantle pallial of twenty Pinctada fucata). Approximately 20 μg of mRNA was obtained through a purification of poly(A)⁺ mRNA by applying these RNA to an oligo-dT-cellulose column (a purification kit for mRNA: Pharmacia). When these poly(A)⁺ mRNA were applied to an agarose electrophoresis, a band was formed around 18 s.

mRNA obtained from the mantle pallial and applied to the gel electrophoresis was transferred to a nitocellulose filter. Then, when the labelled DNA probes aforenoted were hybridized to the filter, a band indicating positive signal was appeared around 2.3 kb. Such signal had not been detected in the control RNA extracted from the whole body of Pinctada fucata. Therefore, it was demonstrated that only RNA sample obtained from the mantle pallial have mRNA of nacrein which can specifically hybridize to the DNA probes.

(3) Construction of cDNA Library

cDNA from mRNA obtained from the mantle pallial was prepared with cDNA synthesis kit of Pharmacia. Adapter having EcoRI-NotI site is linked to both ends of synthesized cDNA. cDNA so made was cloned with λgt10 as a vector and was packaged. Then, the plaque was produced thereby in E. coli Hf1·NM514 strain. As a result, approximately 270,000 pfu phages were obtained from 2 μg of 20 μg mRNA so purified.

The phages were inoculated into plastic dishes of 9 cm diameter to get approximately 10,000 plaques per one dish, and the appeared plaques were transferred to a nitrocellulose filter. Five filters collected from five dishes were plaque hybridized with the labelled probes noted above, then six independent spots indicating positive signal were obtained. Each plaque corresponding to each of these spots was collected, then, screening (selection) on the plaques indicating positive signal was repeatedly purified them.

After multiplication of the purified phage clones in E. coli Hf1 NM514 strain, DNA extracted from each of phage clones and NotI digested were applied to a gel electrophoresis.

Since it came to know that cloned target cDNA fragments have one EcoRI restriction site, DNA extracted from each of the clones was digested with NotI. When such NotI digested gel patterns were transferred to nitrocellulose filter and were hybridized with the labelled probes noted above, DNA fragments of 2.3 kb indicated positive signal. Accordingly, it was concluded that these DNA fragments are cDNA of the nacrein.

EXAMPLE 4 Sequencing on Total Base Sequence of Nacrein cDNA

DNA fragments determined in Example 3 as cDNA of nacrein were subcloned into the plasmid pBluescript. Of the six clones, subcloning on four clones were succeeded and were designated respectively as CλN2, CλN5, CλN6 and CλN9. There are common pattern in the restriction map (a map of restriction sites) prepared for these fragments.

FIG. 9 is a map on CλN6. In FIG. 9, PBKS (Stratagene) is one of the plasmid pBluescript to clone E. coli, and points of N, E, B and S denoted in the figure are restriction sites by restriction enzymes NotI, EcoRI, BamHI and SacI respectively.

Since CλN6 illustrated in FIG. 9 could be divided into five fragments, each fragment was subcloned into plasmid pUC19 for the base sequence determination. Since SacI-EcoRI fragments (1.6 kb) without restricting by BamHI are too long to directly sequence it, some deletion strains thereof were prepared by subcloning these fragments into pUC19 and deleting the same, little by little, with Exo III and Bal 31 nuclease. All of these fragments were applied to DNA sequencer (No.373S: Applied Biosystems) to analyze the base sequences, then the total base sequence and the amino acids sequence (SEQ ID No.: 6) in the DNA fragments inserted into CλN6 were determined with software for processing gene information (GENETYX-MAC) by arranging and analyzing data so obtained.

The following facts are clarified through a study of the total base sequence and the amino acids sequence set out in SEQ ID No.: 6.

(1) Coding region is consisting of 447 amino acids (1341 bases) started from methionine [1st amino acid] of 22nd˜24th bases and ended at lysine [447th amino acid] of 1360th˜1362th bases. Base sequences corresponding to this coding region is set out in SEQ ID No.: 7, while amino acids sequence corresponding to the mature nacrein proteins (coding region without the signal peptide) is set out in SEQ ID No.: 8.

(2) Non-Coding region is positioned from TAG (amber nonsense codon) of 1363rd˜1365th bases and contains much bases of AT.

(3) Signal sequence. A sequence is started from methionine [1st amino acid] coded by ATG of 22nd˜24th bases and ended at glycine [17th amino acid] coded by GGC of 70th˜72nd bases. This sequence is ended with glycine and contains a cluster of hydrophobic amino acids together with that of hydrophilic amino acids subsequent thereto. This portion therefore seems to be a signal sequence of this protein.

(4) Sense strands (SEQ ID No.:4) corresponding to 44 mer DNA probes (SEQ ID No.:5) and synthesized to get the cDNA clone are positioned between G (glycine) of 73th base and G (glycine) of 117th base in SEQ ID No.:6.

(5) Nacrein is Ca²⁺ -binding protein. In general, Gly-Asx surrounded by hydrophobic amino acids, so called EF hand structure, have been known as Ca²⁺ -binding sites. As a similar structure, 242nd˜323rd amino acids sequence corresponding to 745th˜990th bases of SEQ ID No.:6 is a quite unique sequence and have 27 repeat units of Gly-Asx-Asn- (Asx; Asp or Asn) sequence (SEQ ID No.:9). This is a surprising discovery.

(6) Sequence search was conducted in data base on amino acids sequence for the proteins (Swissprot protein data base). The results indicated that nacrein have homology with the carbonic anhydrase (hereinafter referred to as "CA"), in particular, with CAII of human erythrocyte (See, FIG. 10). The carbonic anhydrase catalyze a chemical reaction to be processed along with the following formula [I]. ##EQU1##

Then, the presence of enzymatic activity on nacrein protein was determined in accordance with the following procedures.

Necessary time (T) to reach at pH 7.3 was seen by adding 2 ml of water saturated with carbon dioxide to 3 ml of 20 mM Veronal buffer (pH 8.3) under the presence of 10 μl of the proteins (enzymes) with continuous agitation. Chemical reaction was processed at the temperature of 0° C., because the reaction rate is too large at room temperature. Further, control time (T₀) to reach at pH 7.3 without an enzyme was also seen.

Activity of the enzyme will be derived according to the following formula [II] by putting T and To thereinto.

    Activity (unit)=(T.sub.0 -T)/T                             [II]

Results obtained along with aforenoted procedures are shown in the following Table 1.

                  TABLE 1                                                          ______________________________________                                         DETERMINATION ON CARBONIC ANHYDRASE ACTIVITY                                                     Amount           Specific Activity                                                               Sample (μg) T (sec.) (Unit/mg)          ______________________________________                                         --            --       105    (=T.sub.0)                                                                          --                                            BECA 0.1 30  2.5 × 10.sup.4                                              BECA (heat-inactivated) 0.1 130  --                                            Nacrein 0.8 45  1.6 × 10.sup.3                                           Nacrein 1.6 24  2.1 × 10.sup.3                                           Nacrein (heat-inactivated) 0.8 140  --                                         BSA 4.0 120  --                                                              ______________________________________                                          BECA: Bovine Erythrocyte Carbonic Anhydrase                                    BSA: Bovine Serum Albumin                                                

Data listed in Table is an average of two individual experiments.

Apparently from the results shown in Table 1, the nacrein is an enzyme protein having an activity of carbonic anhydrase.

In light of the results noted above, nacrein is the structural element of the pearl layer and is also the functional protein which can synthesize aragonite crystal of the calcium carbonate from Ca²⁺ and carbonate ion respectively dissolved in the sea water.

(7) This protein may have molecular weight of 50,000, if it is calculated based on the molecular weight of amino acids in the coding region without the signal sequence. There is difference of about 10,000 in molecular weight between the calculated weight and that of about 60,000 determined by mobility at SDS-PAGE.

EXAMPLE 5 Expression of Nacrein in Host [E. coli]

Since the base sequence of nacrein cDNA were determined in the previous Example, gene expression of such cDNA was tried in the cell of E. coli with a vector having the cDNA linked thereto.

First of all, pT7-7 [Studier, F. W. et al., Methods Enzymol. 185, 60-89 (1991)] was selected as a vector for the gene expression. Then, PCR-amplified open reading frame of the nacrein was inserted at NdeI-EcoRI site as shown in FIG. 11.

Apparently from the structure of the vector so constructed, expression of the inserted gene is controlled by promoter .O slashed.10 to be functioned with T7RNA polymerase positioned prior to the gene. On the other hand, since expression of T7RNA polymerase can be induced in E. coli BL21 (λDE3) strain by an addition of IPTG (isopropylthiogalactoside), the synthesis of the nacrein was studied by preparing transformants of this strain transformed with the plasmid noted above.

An anti-rabitt-nacrein-antibody was used to detect and determined the quantity of the nacrein. The antibody is an anti-serum produced by preparing an unit preparation for injection consisting of a mixture (an antigen) of equal volume of 1 ml of nacrein sample (20 μg/ml protein) purified according to the Example 1 and an adjuvant (Wako Junyaku), immunizing twice rabbits with the unit preparation every 3 weeks, and collecting blood on one month after then. The antibody can detect the nacrein even if it is diluted to 1/10,000.

Transformed bacterial cells, which were induced by IPTG and thereby synthesized the nacrein, was solved by SDS. All of the solved bacterium were applied to SDS-electrophoresis, and were transferred to PVDF membrane filter (Immobilon P) with a blotting divice (Nihon-Eido Co., Ltd.).

Then the sample were washed with anti-babbit-serum, then with goat-anti-rabbit IgG antibody labelled with peroxidase of horse radish, and color was developed with DAB (3,3'-diaminobenzidine).

With respect to each of the isolated strains, positive spots having the reactivity with the antibody in the control lane (-) without IPTG were not detected. In contrast thereto, dark black band was clearly detected in the experimental lane (+) induced with IPTG (FIG. 12-I).

These results suggest that the nacrein proteins (several percent of the total proteins deduced from the other data on stainability with Coomassie Blue) would be produced in the cell of E. coli. These proteins may be biosynthesized in the cell of yeast or silkworm according to the same procedure. If the industrial production thereof is planned, it will be considered as to which system is the most preferable to effectively synthesize natural-like proteins and is advantageous to the purification of the products.

When the biosynthesized nacrein (Band A) of this Example and the natural nacrein (Example 1: Band C) are applied to electriphoresis and are compared (FIG. 12-II), molecular weight of the natural nacrein is apparently larger than that of the biosynthesized nacrein. This may due to a modification after the translation. In view of the thesis [Tetsuro Samata: Venus 47, 127-140 (1988)] suggesting that these proteins may glycoprotein, although PAS-staining had been performed to see the presence of the glycosaccharides and restriction by N-glucosidase, an expected result could not be obtained. Besides the molecular weight, there was considerable difference on pI between the proteins biosynthesized in E. coli and the natural nacrein proteins. Further, in light of the difference on stainability by Stains-all (an indicator of Ca²⁺ -binding activity), acid groups have been bonded thereto by β-carboxylating asparatic acids in the repeated region of sequence of Gly-Asx-Asn (SEQ ID NO:9). Therefore, pI of the natural nacrein molecule and Ca²⁺ -binding activity comes to be larger.

Taking such conditions into the consideration, to realize the large scale production of the nacrein molecule similar to the natural nacrein, it would be necessary that the nacrein cDNA was introduced in the eucaryotic host like yeast or silkworm and was expressed therein.

INDUSTRIAL APPLICABILITY

As stated above, according to the present invention, prior producing technique depended on the environmental conditions may be unnecessary, and pearl proteins can be produced artificially. Further, desirous effects, like an industrial mass production of the pearl, can also be expected by utilizing the gene structure analayzed by the inventor which is involving in a formation of pearl proteins.

    __________________________________________________________________________     #             SEQUENCE LISTING                                                    - -  - - (1) GENERAL INFORMATION:                                              - -    (iii) NUMBER OF SEQUENCES: 9                                            - -  - - (2) INFORMATION FOR SEQ ID NO:1:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 15 amino - #acids                                                  (B) TYPE: amino acid                                                           (C) STRANDEDNESS: Not R - #elevant                                             (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                - - Ala Ser Met Phe Lys Met Asp Xaa Tyr Met As - #p Xaa Gly Xaa Arg          1               5   - #                10  - #                15                - -  - - (2) INFORMATION FOR SEQ ID NO:2:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 15 amino - #acids                                                  (B) TYPE: amino acid                                                           (C) STRANDEDNESS: Not R - #elevant                                             (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: peptide                                            - -     (ix) FEATURE:                                                                   (A) NAME/KEY: misc.sub.-- - #feature                                           (B) LOCATION: 1                                                                (D) OTHER INFORMATION: - #/note= "Amino Acid of this position                       is Ser, - #Ala, or Gly"                                          - -     (ix) FEATURE:                                                                   (A) NAME/KEY: misc.sub.-- - #feature                                           (B) LOCATION: 8                                                                (D) OTHER INFORMATION: - #/note= "Amino Acid of this position                       is His - #or Asp"                                                - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                - - Xaa His Met Phe Lys His Asp Xaa Tyr Met As - #p Asp Gly Val Arg           1               5   - #                10  - #                15                - -  - - (2) INFORMATION FOR SEQ ID NO:3:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 15 amino - #acids                                                  (B) TYPE: amino acid                                                           (C) STRANDEDNESS: Not R - #elevant                                             (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                - - Ala Ser Met Phe Lys His Asp His Tyr Met As - #p Asn Gly Val Arg           1               5   - #                10  - #                15                - -  - - (2) INFORMATION FOR SEQ ID NO:4:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 44 base - #pairs                                                   (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: other nucleic acid                                          (A) DESCRIPTION: /desc - #= "Synthesized DNA"                         - -     (iv) ANTI-SENSE: NO                                                    - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                - - KCNCAYATGT TYAARMWBGA YSAYTAYATG GAYGAYGGNG TNMG   - #                       - # 44                                                                       - -  - - (2) INFORMATION FOR SEQ ID NO:5:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 44 base - #pairs                                                   (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: other nucleic acid                                          (A) DESCRIPTION: /desc - #= "Synthesized DNA"                         - -     (iv) ANTI-SENSE: YES                                                   - -     (ix) FEATURE:                                                                   (A) NAME/KEY: misc.sub.-- - #feature                                           (B) LOCATION: 42                                                               (D) OTHER INFORMATION: - #/note= "N = INOSINE"                        - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                - - CKNACNCCRT CRTCCATRTA RTSRTCVWKY TTRAACATRT GNSW   - #                       - # 44                                                                       - -  - - (2) INFORMATION FOR SEQ ID NO:6:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 2363 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 22..1362                                                - -     (ix) FEATURE:                                                                   (A) NAME/KEY: sig.sub.-- - #peptide                                            (B) LOCATION: 22..72                                                  - -     (ix) FEATURE:                                                                   (A) NAME/KEY: binding s - #ite                                                 (B) LOCATION: 73..120                                                 - -     (ix) FEATURE:                                                                   (A) NAME/KEY: repeat.sub.-- - #region                                          (B) LOCATION: 745..990                                                - -     (ix) FEATURE:                                                                   (A) NAME/KEY: repeat.sub.-- - #unit                                            (B) LOCATION: 745..748                                                - -     (ix) FEATURE:                                                                   (A) NAME/KEY: active si - #te                                                  (B) LOCATION: 1144..1287                                              - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                - - TAGTAAATGT GAAGATTGGT G ATG TAT CTT CAT TTG ACT - #GCC CTA TGT GTT            51                                                                                           - #      Met Tyr Leu His Leu Thr Ala - #Leu Cys Val                            - #        1          - #     5             - #     10        - - GTT ATT CCG CTG TGT TAT GGC GCC TCC ATG TT - #T AAA CAT GAC CAC TAC            99                                                                        Val Ile Pro Leu Cys Tyr Gly Ala Ser Met Ph - #e Lys His Asp His Tyr                             15 - #                 20 - #                 25               - - ATG GAC AAT GGT GTG AGG TAT CCT AAT GGT GA - #C GGA ATC TGT AAA CAA           147                                                                        Met Asp Asn Gly Val Arg Tyr Pro Asn Gly As - #p Gly Ile Cys Lys Gln                         30     - #             35     - #             40                   - - TTG AAT GAA ACC AAA TGT GAT GCA GGG TTT AG - #C TAT GAT AGG AGT ATA           195                                                                        Leu Asn Glu Thr Lys Cys Asp Ala Gly Phe Se - #r Tyr Asp Arg Ser Ile                     45         - #         50         - #         55                       - - TGT GAA GGT CCT CAT TAT TGG CAC ACC ATA TC - #G AAA TGC TTC ATT GCA           243                                                                        Cys Glu Gly Pro His Tyr Trp His Thr Ile Se - #r Lys Cys Phe Ile Ala                 60             - #     65             - #     70                           - - TGT GGA ATT GGA CAG AGA CAA TCT CCA ATC AA - #C ATC GTT TCT TAT GAT           291                                                                        Cys Gly Ile Gly Gln Arg Gln Ser Pro Ile As - #n Ile Val Ser Tyr Asp             75                 - # 80                 - # 85                 - # 90        - - GCT AAA TTT CGT CAG CGT TTG CCA AAA TTG AA - #A TTC AAG CCA CAT ATG           339                                                                        Ala Lys Phe Arg Gln Arg Leu Pro Lys Leu Ly - #s Phe Lys Pro His Met                             95 - #                100 - #                105               - - GAG AAA TTA AAA ACA GAA GTG ACC AAT CAT CA - #G AAC CGA GCT CCA GAG           387                                                                        Glu Lys Leu Lys Thr Glu Val Thr Asn His Gl - #n Asn Arg Ala Pro Glu                        110      - #           115      - #           120                   - - TTC GAG CCA GAG GAT GGG GAA AAT CTG TAC GT - #G AAG CTA AAT AAC CTA           435                                                                        Phe Glu Pro Glu Asp Gly Glu Asn Leu Tyr Va - #l Lys Leu Asn Asn Leu                    125          - #       130          - #       135                       - - GTG GAC GGT CAT TAT AAA TTC CAT AAT CTT CA - #C GTT CAT AAT GGT AGA           483                                                                        Val Asp Gly His Tyr Lys Phe His Asn Leu Hi - #s Val His Asn Gly Arg                140              - #   145              - #   150                           - - ACC AGA CGT AAG GGA TCA GAA CAC AGT GTT AA - #C GGT CGT TTC ACA CCT           531                                                                        Thr Arg Arg Lys Gly Ser Glu His Ser Val As - #n Gly Arg Phe Thr Pro            155                 1 - #60                 1 - #65                 1 -       #70                                                                               - - ATG GAG GCT CAT TTG GTT TTC CAT CAT GAT GA - #T CAA ACA CAC TTT         GAA      579                                                                     Met Glu Ala His Leu Val Phe His His Asp As - #p Gln Thr His Phe Glu                           175  - #               180  - #               185               - - CCT ACA CGC ACT AAG CTG GGA GGA GCA TTC CC - #T GGT CAT AAC GAT TTT           627                                                                        Pro Thr Arg Thr Lys Leu Gly Gly Ala Phe Pr - #o Gly His Asn Asp Phe                        190      - #           195      - #           200                   - - GTC GTC GTT GGA GTT TTT CTT GAG GTC GGA GA - #T GAC GGC TTT GGC GAC           675                                                                        Val Val Val Gly Val Phe Leu Glu Val Gly As - #p Asp Gly Phe Gly Asp                    205          - #       210          - #       215                       - - GAA CCG GAT GAC GAA GAA TGT AAA CAC ATC TT - #A AAG GGA CAT CAC CCT           723                                                                        Glu Pro Asp Asp Glu Glu Cys Lys His Ile Le - #u Lys Gly His His Pro                220              - #   225              - #   230                           - - GAT AAT AAC GAG AAC GGC AAT GGA GAC AAT GG - #C AAT AAC GGC TAC AAT           771                                                                        Asp Asn Asn Glu Asn Gly Asn Gly Asp Asn Gl - #y Asn Asn Gly Tyr Asn            235                 2 - #40                 2 - #45                 2 -       #50                                                                               - - GGG GAC AAC GGT AAC AAT GGT GAC AAC GGC AA - #T AAC AGC TAC AAT         GGG      819                                                                     Gly Asp Asn Gly Asn Asn Gly Asp Asn Gly As - #n Asn Ser Tyr Asn Gly                           255  - #               260  - #               265               - - GAC AAC GGT AAC AAT GGT GTC AAC GGC AAT AA - #C GGC TAC AAT GGG GAC           867                                                                        Asp Asn Gly Asn Asn Gly Val Asn Gly Asn As - #n Gly Tyr Asn Gly Asp                        270      - #           275      - #           280                   - - AAC GGT AAC AAT GGA GAC AAC GGC AAT AAC GG - #C TAC AAT GGG GAC AAC           915                                                                        Asn Gly Asn Asn Gly Asp Asn Gly Asn Asn Gl - #y Tyr Asn Gly Asp Asn                    285          - #       290          - #       295                       - - GGT AAC AAT GGT GAC AAC GGC AAT AAC GGT GA - #A AAC GGC AAT AAC GGT           963                                                                        Gly Asn Asn Gly Asp Asn Gly Asn Asn Gly Gl - #u Asn Gly Asn Asn Gly                300              - #   305              - #   310                           - - GAA AAC GGC AAT AAC GGT GAA AAT GGT CAC AA - #A CAC GGA TGT CGG GTA          1011                                                                        Glu Asn Gly Asn Asn Gly Glu Asn Gly His Ly - #s His Gly Cys Arg Val            315                 3 - #20                 3 - #25                 3 -       #30                                                                               - - AAG AAA GCA AAG CAT CTC AGT AGG ATC CTG GA - #A TGT GCT TAT AGA         AAC     1059                                                                     Lys Lys Ala Lys His Leu Ser Arg Ile Leu Gl - #u Cys Ala Tyr Arg Asn                           335  - #               340  - #               345               - - GAT AAG GTC AGA GAG TTC AAG AAA GTT GGA GA - #A GAG GAA GGG TTA GAT          1107                                                                        Asp Lys Val Arg Glu Phe Lys Lys Val Gly Gl - #u Glu Glu Gly Leu Asp                        350      - #           355      - #           360                   - - GTT CAT CTA ACA CCG GAG ATG GCT TTG CCG CC - #A CTG AAG TAC AGA CAT          1155                                                                        Val His Leu Thr Pro Glu Met Ala Leu Pro Pr - #o Leu Lys Tyr Arg His                    365          - #       370          - #       375                       - - TAC TAT ACA TAC GAG GGA TCC CTG ACC ACT CC - #C CCG TGT ACA GAG TCT          1203                                                                        Tyr Tyr Thr Tyr Glu Gly Ser Leu Thr Thr Pr - #o Pro Cys Thr Glu Ser                380              - #   385              - #   390                           - - GTC CTC TGG GTT GTT CAA AAA TGC CAT GTG CA - #G GTG TCA AGA AGG GTT          1251                                                                        Val Leu Trp Val Val Gln Lys Cys His Val Gl - #n Val Ser Arg Arg Val            395                 4 - #00                 4 - #05                 4 -       #10                                                                               - - CTT CAT GCA TTA CGA AAT GTT GAA GGA TAT AA - #A GAT GGT ACC ACA         CTA     1299                                                                     Leu His Ala Leu Arg Asn Val Glu Gly Tyr Ly - #s Asp Gly Thr Thr Leu                           415  - #               420  - #               425               - - AGA AAG TAT GGA ACT AGA CGT CCA ACG CAA AA - #G AAT AAA GTT ACT GTG          1347                                                                        Arg Lys Tyr Gly Thr Arg Arg Pro Thr Gln Ly - #s Asn Lys Val Thr Val                        430      - #           435      - #           440                   - - TAC AAA AGC TTC AAA TAGTTGACAT AGTTTTTGTT CTTTTCCTT - #A TAGAGACATG          1402                                                                        Tyr Lys Ser Phe Lys                                                                    445                                                                     - - TAACACAGCC AATTATGTTT CATATGTAAT CCATGTAAAA TACAGGATCT TT -              #ACATAAAT   1462                                                                  - - ATTCATGTGA AACAAGCACG AACATTAAAG GACTAGGTGC GCTAACCCCT TA -             #TATCGGCC   1522                                                                  - - CTATAATTTC GACGAGAAAT GCTTTTAATA AACAAACTAT TAATTATAGC TT -             #TTTGCAAT   1582                                                                  - - GTTGAATGTT TGAGAAAATA CCGCATCATA TTTTTTAGCC CTCGTAACGT CA -             #CGCGAGTG   1642                                                                  - - ATGTATGATG TCATGTTCTG AAAGTCATTT GCCCTGAATG ACGCAAAACA AA -             #TGAGAATC   1702                                                                  - - ATCGTATTTT ACATACAAAT CTTCAAATTC ATCTGCGATT CAGGCCTCGA AC -             #ACGATATT   1762                                                                  - - TTTTATGCAA ATTTAAAGGC CGATCAAAAA TCCATCGATT AGTACAAATA TT -             #ATCGTGGG   1822                                                                  - - CAATTAAGGC CTGGAACGAT ACTTAATTTC ATAAATTTTA ATCGAAATTT CG -             #CTGATTTA   1882                                                                  - - TTGATATTTT CAATGAGTTT CAACGTTTTA GACATTTTTT TGTAATATTC AG -             #TATAGGAC   1942                                                                  - - TATGAAATCA AAAAAAGCTT TCCTGATATG GATTCACCAT ACATTTAACA TT -             #TCAAAAAC   2002                                                                  - - TAGAATATTA TGGATATATG AACAACTTTG AAAATGGGGC CGATATGGCA GG -             #TTACCGAA   2062                                                                  - - CCTACTTCTT TTTATCAAAT TTTTTACATG AAATTCATGG GAAGTTTCCG AC -             #ATCAATTT   2122                                                                  - - CATGTGAATT CTATATCGCA TGAAGGTCAC AAAGAAAATT TCATGTAAAA TT -             #CATGCGAA   2182                                                                  - - GGAAATTCAT GTGAAACTCA TGTGAAATAT TTTTCACATA AATCTTAAGT GA -             #AAAGTATA   2242                                                                  - - TAAATTTCAC AACTTTCATG TGAAATTTAA GTGATGCTCA TTTTGTATGG AT -             #TTCATGTG   2302                                                                  - - AGGCATAATT GACTGCTTGT ACTATGTAAT TAGAACAAAA TGTCAAATAT TT -             #AATAAATG   2362                                                                  - - A                  - #                  - #                  - #                  2363                                                                   - -  - - (2) INFORMATION FOR SEQ ID NO:7:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1341 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: sig.sub.-- - #peptide                                            (B) LOCATION: 21..51                                                  - -     (ix) FEATURE:                                                                   (A) NAME/KEY: binding s - #ite                                                 (B) LOCATION: 52..99                                                  - -     (ix) FEATURE:                                                                   (A) NAME/KEY: repeat.sub.-- - #region                                          (B) LOCATION: 742..969                                                - -     (ix) FEATURE:                                                                   (A) NAME/KEY: repeat.sub.-- - #unit                                            (B) LOCATION: 724..727                                                - -     (ix) FEATURE:                                                                   (A) NAME/KEY: active si - #te                                                  (B) LOCATION: 1123..1266                                              - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                - - ATGTATCTTC ATTTGACTGC CCTATGTGTT GTTATTCCGC TGTGTTATGG CG -              #CCTCCATG     60                                                                  - - TTTAAACATG ACCACTACAT GGACAATGGT GTGAGGTATC CTAATGGTGA CG -             #GAATCTGT    120                                                                  - - AAACAATTGA ATGAAACCAA ATGTGATGCA GGGTTTAGCT ATGATAGGAG TA -             #TATGTGAA    180                                                                  - - GGTCCTCATT ATTGGCACAC CATATCGAAA TGCTTCATTG CATGTGGAAT TG -             #GACAGAGA    240                                                                  - - CAATCTCCAA TCAACATCGT TTCTTATGAT GCTAAATTTC GTCAGCGTTT GC -             #CAAAATTG    300                                                                  - - AAATTCAAGC CACATATGGA GAAATTAAAA ACAGAAGTGA CCAATCATCA GA -             #ACCGAGCT    360                                                                  - - CCAGAGTTCG AGCCAGAGGA TGGGGAAAAT CTGTACGTGA AGCTAAATAA CC -             #TAGTGGAC    420                                                                  - - GGTCATTATA AATTCCATAA TCTTCACGTT CATAATGGTA GAACCAGACG TA -             #AGGGATCA    480                                                                  - - GAACACAGTG TTAACGGTCG TTTCACACCT ATGGAGGCTC ATTTGGTTTT CC -             #ATCATGAT    540                                                                  - - GATCAAACAC ACTTTGAACC TACACGCACT AAGCTGGGAG GAGCATTCCC TG -             #GTCATAAC    600                                                                  - - GATTTTGTCG TCGTTGGAGT TTTTCTTGAG GTCGGAGATG ACGGCTTTGG CG -             #ACGAACCG    660                                                                  - - GATGACGAAG AATGTAAACA CATCTTAAAG GGACATCACC CTGATAATAA CG -             #AGAACGGC    720                                                                  - - AATGGAGACA ATGGCAATAA CGGCTACAAT GGGGACAACG GTAACAATGG TG -             #ACAACGGC    780                                                                  - - AATAACAGCT ACAATGGGGA CAACGGTAAC AATGGTGTCA ACGGCAATAA CG -             #GCTACAAT    840                                                                  - - GGGGACAACG GTAACAATGG AGACAACGGC AATAACGGCT ACAATGGGGA CA -             #ACGGTAAC    900                                                                  - - AATGGTGACA ACGGCAATAA CGGTGAAAAC GGCAATAACG GTGAAAACGG CA -             #ATAACGGT    960                                                                  - - GAAAATGGTC ACAAACACGG ATGTCGGGTA AAGAAAGCAA AGCATCTCAG TA -             #GGATCCTG   1020                                                                  - - GAATGTGCTT ATAGAAACGA TAAGGTCAGA GAGTTCAAGA AAGTTGGAGA AG -             #AGGAAGGG   1080                                                                  - - TTAGATGTTC ATCTAACACC GGAGATGGCT TTGCCGCCAC TGAAGTACAG AC -             #ATTACTAT   1140                                                                  - - ACATACGAGG GATCCCTGAC CACTCCCCCG TGTACAGAGT CTGTCCTCTG GG -             #TTGTTCAA   1200                                                                  - - AAATGCCATG TGCAGGTGTC AAGAAGGGTT CTTCATGCAT TACGAAATGT TG -             #AAGGATAT   1260                                                                  - - AAAGATGGTA CCACACTAAG AAAGTATGGA ACTAGACGTC CAACGCAAAA GA -             #ATAAAGTT   1320                                                                  - - ACTGTGTACA AAAGCTTCAA A           - #                  - #                     1341                                                                      - -  - - (2) INFORMATION FOR SEQ ID NO:8:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 430 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: Not R - #elevant                                             (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:                                - - Ala Ser Met Phe Lys His Asp His Tyr Met As - #p Asn Gly Val Arg Tyr       1               5   - #                10  - #                15                - - Pro Asn Gly Asp Gly Ile Cys Lys Gln Leu As - #n Glu Thr Lys Cys Asp                   20      - #            25      - #            30                    - - Ala Gly Phe Ser Tyr Asp Arg Ser Ile Cys Gl - #u Gly Pro His Tyr Trp               35          - #        40          - #        45                        - - His Thr Ile Ser Lys Cys Phe Ile Ala Cys Gl - #y Ile Gly Gln Arg Gln           50              - #    55              - #    60                            - - Ser Pro Ile Asn Ile Val Ser Tyr Asp Ala Ly - #s Phe Arg Gln Arg Leu       65                  - #70                  - #75                  - #80         - - Pro Lys Leu Lys Phe Lys Pro His Met Glu Ly - #s Leu Lys Thr Glu Val                       85  - #                90  - #                95                - - Thr Asn His Gln Asn Arg Ala Pro Glu Phe Gl - #u Pro Glu Asp Gly Glu                   100      - #           105      - #           110                   - - Asn Leu Tyr Val Lys Leu Asn Asn Leu Val As - #p Gly His Tyr Lys Phe               115          - #       120          - #       125                       - - His Asn Leu His Val His Asn Gly Arg Thr Ar - #g Arg Lys Gly Ser Glu           130              - #   135              - #   140                           - - His Ser Val Asn Gly Arg Phe Thr Pro Met Gl - #u Ala His Leu Val Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - His His Asp Asp Gln Thr His Phe Glu Pro Th - #r Arg Thr Lys Leu         Gly                                                                                              165  - #               170  - #               175              - - Gly Ala Phe Pro Gly His Asn Asp Phe Val Va - #l Val Gly Val Phe Leu                   180      - #           185      - #           190                   - - Glu Val Gly Asp Asp Gly Phe Gly Asp Glu Pr - #o Asp Asp Glu Glu Cys               195          - #       200          - #       205                       - - Lys His Ile Leu Lys Gly His His Pro Asp As - #n Asn Glu Asn Gly Asn           210              - #   215              - #   220                           - - Gly Asp Asn Gly Asn Asn Gly Tyr Asn Gly As - #p Asn Gly Asn Asn Gly       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Asp Asn Gly Asn Asn Ser Tyr Asn Gly Asp As - #n Gly Asn Asn Gly         Val                                                                                              245  - #               250  - #               255              - - Asn Gly Asn Asn Gly Tyr Asn Gly Asp Asn Gl - #y Asn Asn Gly Asp Asn                   260      - #           265      - #           270                   - - Gly Asn Asn Gly Tyr Asn Gly Asp Asn Gly As - #n Asn Gly Asp Asn Gly               275          - #       280          - #       285                       - - Asn Asn Gly Glu Asn Gly Asn Asn Gly Glu As - #n Gly Asn Asn Gly Glu           290              - #   295              - #   300                           - - Asn Gly His Lys His Gly Cys Arg Val Lys Ly - #s Ala Lys His Leu Ser       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Arg Ile Leu Glu Cys Ala Tyr Arg Asn Asp Ly - #s Val Arg Glu Phe         Lys                                                                                              325  - #               330  - #               335              - - Lys Val Gly Glu Glu Glu Gly Leu Asp Val Hi - #s Leu Thr Pro Glu Met                   340      - #           345      - #           350                   - - Ala Leu Pro Pro Leu Lys Tyr Arg His Tyr Ty - #r Thr Tyr Glu Gly Ser               355          - #       360          - #       365                       - - Leu Thr Thr Pro Pro Cys Thr Glu Ser Val Le - #u Trp Val Val Gln Lys           370              - #   375              - #   380                           - - Cys His Val Gln Val Ser Arg Arg Val Leu Hi - #s Ala Leu Arg Asn Val       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Glu Gly Tyr Lys Asp Gly Thr Thr Leu Arg Ly - #s Tyr Gly Thr Arg         Arg                                                                                              405  - #               410  - #               415              - - Pro Thr Gln Lys Asn Lys Val Thr Val Tyr Ly - #s Ser Phe Lys                           420      - #           425      - #           430                   - -  - - (2) INFORMATION FOR SEQ ID NO:9:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 3 amino - #acids                                                   (B) TYPE: amino acid                                                           (C) STRANDEDNESS: Not R - #elevant                                             (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:                                - - Gly Asx Asn                                                              __________________________________________________________________________ 

I claim:
 1. An isolated DNA molecule encoding a nacrein pearl protein, wherein said DNA molecule comprises the base sequence depicted SEQ ID NO:7.
 2. The DNA molecule of to claim 1, wherein said protein is nacrein protein produced by Pinctada fucata.
 3. The DNA molecule of to claim 2, wherein the molecular weight of said nacrein protein is 60,000 as determined by SDS-PAGE.
 4. An isolated nacrein protein derived from a pearl, wherein said protein comprises the amino acid sequence depicted in SEQ ID NO:8.
 5. The protein of claim 4, wherein said protein is nacrein protein produced by Pinctada fucata.
 6. The protein of claim 4 or 5, wherein said amino acid sequence is encoded by the base sequence depicted in SEQ ID NO:7.
 7. The protein of claim 4 or 5 wherein the molecular weight of said nacrein protein is 60,000 as determined by SDS-PAGE.
 8. A method for isolating nacrein protein derived from Pinctada fucata, said method comprising(a) extracting pearl protein from pearl layer of Pinctada fucata; (b) collecting fractions containing the protein in the molecular weight of 60,000 as determined by applying the pearl protein to SDS-PAGE; (c) synthesizing probes encoding N-terminal amino acids sequence of said pearl protein; (d) cloning cDNA to be hybridized with said probes from cDNA library constructed based on mRNA obtained from mantle of Pinctada fucata; and (e) expressing nacrein proteins by introducing said cDNA into a host cell like Escherichia coli.
 9. Method according to claim 8, wherein said host is a cell of an organism selected from the group consisting of Escherichia coli, yeast and silkworm.
 10. Method according to claim 9, wherein said host is a cell of Escherichia coli BL21(λDE3).
 11. Protein according to claim 6 wherein the molecular weight of said nacrein protein is 60,000 as determined by SDS-PAGE. 